1. Field of Invention
The present invention relates to a method of forming a via plug or a contact plug, and more particularly to a method of removing a keyhole formation within a tungsten plug inside a via hole or a contact hole after a chemical-mechanical polishing operation is performed.
2. Description of Related Art
Contact plugs and via plugs (hereinafter "plugs") are devices for interconnecting different conducting layers (metallic layers) in an integrated circuit component. A plug is manufactured by first forming an inter-layer dielectric above a first conductive layer, and then selectively etching the inter-layer dielectric to form a contact hole exposing portions of the first conducting area. Then, a barrier layer and a glue layer are formed lining the contact hole. Subsequently, metal, such as tungsten, is deposited into the contact hole, and then the metal is etched back to form a conductive plug. Thereafter, a second conductive material is deposited over the inter-layer dielectric to form a second conductive layer. As a result, the two conductive layers are connected through a conductive plug inside a contact hole.
At present, the etching back of the deposited metal to form the conductive plug is typically performed using a chemical-mechanical polishing operation. However, because of the formation of an overhang in the glue layer near the top end of the contact hole, a keyhole is formed in the conductive plug.
FIGS. 1a, 1b, and 1c are cross-sectional views showing the manufacturing progression of a tungsten plug according to a conventional method. To simplify explanations, processes unrelated to the present invention are omitted and the description starts after a conductive layer 10 is formed.
First, as shown in FIG. 1a, an inter-layer dielectric 12 is formed over conductive layer 10. Then, a portion of the inter-layer dielectric 12 is etched to form a contact hole 14 exposing portions of the conductive layer 10.
Next, in FIG. 1b, a diffusion barrier layer 16 and a glue layer 18 are sequentially formed over the inter-layer dielectric 12 and the exposed portions of the conductive layer 10. The diffusion barrier layer 16 can be, for example, a titanium (Ti) layer, and the glue layer 18 can be a titanium nitride (TiN) layer. The diffusion barrier layer 16 and the glue layer 18 serve to prevent a direct contact of the conductive layer 10 with a subsequently formed plug metal layer, and serve to increase the bonding strength between the conductive layer 10 and the subsequently formed plug metal layer.
Thereafter, a metallic layer 20, for example, a tungsten layer having a thickness of about 8000 .ANG., is deposited over the glue layer 18, which also fills the contact hole 14. However, due to the presence of an overhang 18a formed when the glue layer 18 is first formed, a keyhole 22 is formed within the metal layer 20 inside the contact hole 14.
Finally, as shown in FIG. 1c, a chemical-mechanical polishing (CMP) operation is performed to remove the metallic layer 20 above the inter-layer dielectric 12 to form a plug 24. Because of the keyhole 22 formed in the previous operation, a cavity 22a is also formed. Since the cavity 22a inside the metal plug is exposed, slurry from the CMP operation can easily get inside the cavity, causing reliability problems in the subsequently formed integrated circuit. In light of the foregoing, there is a need in the art to provide a method of covering, the plug cavity.